(a) Statement of the Invention
The present invention relates to polymerizable macromolecular monomers and chemically joined, phase separated thermoplastic graft copolymers.
(B) Description of the Prior Art
Polymer technology has developed to a high degree of sophistication and extensive research efforts to this direction are being undertaken to obtain improvements in polymer properties. Some of these efforts lead to polymer materials capable of competing with metals and ceramics in engineering applications.
Attempts have been made to blend two different types of polymers in order to obtain the desired properties of each polymer component in the blend, but these attempts have generally been unsuccessful due to incompatibility. Despite the general acceptance of the fact of incompatibility of polymer pairs, there is much interest in devising means whereby the advantageous properties of combinations of polymers may be combined into one product.
One way in which this objective has been sought involves the preparation of block or graft copolymers. In this way, two different polymeric segments, normally incompatible with one another, are joined together chemically to give a sort of forced compatibility. In such a copolymer, each polymer segment continues to manifest its independent polymer properties. Thus, the block or graft copolymer in many instances possesses a combination of properties not normally found in a homopolymer or a random copolymer.
U.S. Pat. No. 3,235,626 to Waack, assigned to Dow Chemical Company, describes a method for preparing graft copolymers of controlled branch configuration. It is described that graft copolymers are produced by first preparing a prepolymer by reacting a vinyl metal compound with an olefinic monomer to obtain a vinyl terminated prepolymer. After protonation and catalyst removal, the prepolymer is dissolved in an inert solvent with a polymerization catalyst and the prepolymer is thereafter reacted with either a different polymer having a reactive vinyl group or a different vinyl monomer under free-radical conditions.
The limitations on the preparation of these copolymers are mechanistic. Thus, there is no means for controlling the spacing of the sidechains along the backbone chain and the possibility of the sidechains having irregular sizes. Due to the mechanistic limitations of the prior art methods, i.e., the use of an alpha-olefin terminated prepolymer with acrylonitrile or an acrylate monomer under free-radical conditions, complicated mixtures of free homopolymers result.
In view of the above considerations, it would be highly desirable to devise a means for preparing graft copolymers wherein the production of complicated mixtures of free homopolymers is minimized and the beneficial properties of the sidechain and backbone polymer are combined in one product.
It is recognized and documented in the literature, such as R. Waack et al, Polymer, Vol. 2, pp. 365-366 (1961), and R. Waack et al, J. Org. Chem., Vol. 32, pp. 3395-3399 (1967), that vinyl lithium is one of the slowest anionic polymerization initiators. The slow initiator characteristic of vinyl lithium when used to polymerize styrene produces a polymer having a broad molecular weight distribution due to the ratio of the overall rate of propagation of the styryl anion to that of the vinyl lithium initiation. Accordingly, following the practice of U.S. Pat. No. 3,235,626, a graft copolymer having sidechains of uniform molecular weight cannot be prepared.
U.S. Pat. Nos. 3,390,206 and 3,514,500 describe processes for terminating free-radical and ionic polymerized polymers with functional groups which are described as capable of copolymerizing with polymerizable monomers. The functionally terminated prepolymers described by these patentees would be expected to have a broad molecular weight distribution and, therefore, would not be expected to develop ultimate physical properties which are found in polymers formed from prepolymers having narrow molecular weight distribution.
U.S. Pat. No. 3,786,116 to Milkovich and Chiang, granted on Jan. 15, 1974 (which is assigned to the same assignees as the present application, the disclosure of which is incorporated herein by reference) describes phase separated thermoplastic graft copolymers derived from ethylenically unsaturated monomers as the backbone comonomer, and as side chains, copolymerized macromolecular monomers having substantially uniform molecular weight distribution formed from anionically polymerized monomers.
U.S. Pat. No. 3,842,146 to Milkovich and Chiang, granted on Oct. 15, 1974, which is also assigned to the same assignee as the present application (and is also incorporated herein by reference) discloses and claims polymerizable di-block macromolecular monomers of a polymerized monoalkenyl-substituted aromatic hydrocarbon and a polymerized conjugated diene and having a polymerizable end group. The polymerizable di-block macromolecular monomers have a substantially uniform molecular weight distribution. Copolymers of such macromolecular monomers with backbone-forming graft copolymerizing monomers are disclosed and claimed in U.S. Pat. No. 3,862,263, granted Jan. 21, 1975, of Milkovich, Chiang and Schulz, the disclosure of which is also incorporated herein by reference.
These polymerizable macromolecular monomers and graft copolymers overcome many of the aforementioned disadvantages of prior art compositions.
It is a particular object of the present invention to effect even further improvement over the polymeric compositions of the prior art.